Although 80 percent of infectious diseases are initiated at mucosal surfaces, our knowledge of the mechanisms of induction and regulation of mucosal immunity and our ability to exploit the mucosal immune system to prevent infections at or across mucosal surfaces is limited. We have proposed a novel model for regulation of intestinal immunity to enteric viruses by TH1 and TH3, but not TH2 cytokines. We propose that in the absence of TH2 cytokines, TGF-beta (TH3) regulates the antigen-specific IgA response. Studies proposed in this renewal grant application seek to determine the validity of our model. Rotavirus and VLPs will be used to probe the responses to infection or immunization to define the mechanisms and molecules necessary to induce protective intestinal immune responses. It is hypothesized that VLPs and live rotavirus induce protective immunity by different mechanisms since they induce different IgG subclasses and widely divergent IgA responses. It is further hypothesized that VLPs administered intranasally can overcome the compartmentalized immune responses reported to occur in the common mucosal immune system. The specific aims are to determine how differences in protective efficacy of virus and VLPs are regulated by differences in (1) inductive or effector cytokine responses, (2) B cell responses, or (3) homing of memory lymphocytes. Quantitative analysis of the B cell responses and cytokine profiles induced following a variety of mucosal immunization protocols and virus challenge will be performed in normal, specifically-depleted, -upregulated or knockout mice. The results from these basic studies will be relevant to understanding immune regulation and functions at mucosal surfaces and may confirm a novel regulatory mechanism. Further, they will facilitate the design of more effective vaccines for rotavirus and other enteric viruses. The knowledge gained from these basic studies also will be useful in development of new effective vaccine strategies for viral pathogens such as HIV that infect at or invade across mucosal surfaces. The studies proposed in this renewal application are directly relevant to PA-97-101 Basic Mechanisms of Vaccine Efficacy.